As shown in FIG. 14(a), conventionally, in a case where ballast 103 is spread and railroad ties 104 are laid on a track, in order to prevent the track from sinking, ballast 102 immediately under a main line rail 101 to which a load is most strongly applied is dense whereas ballast 103 other than the ballast 102 is comparatively sparse. However, as shown in FIG. 14(b), the ballast 103 immediately under the rail gradually becomes sparse with time by a high vertical load applied thereto via the main line rail 101. Therefore, the ballast 103 immediately under the main line rail 101 is tamped by a tie tamper, a multiple tie tamper, or the like (hereinafter collectively called a “tamping machine”), not shown, at predetermined time intervals or the like in order to prevent a filling density of the ballast from becoming low.
As shown in FIGS. 15(a) and 15(b), a safety rail 105 may be laid along the main line rail 101 for the purpose of preventing a derailed vehicle from seriously deviating to an outer side of the track and minimizing damages of the derailment even in a case where a train runs on, for example, a curved track and its wheel has derailed from the main line rail 101. The safety rail 105 may be laid on a track inner side of the main line rail 101. Moreover, at a place where rocks or snow frequently fall or at a place where the safety rail 105 is especially required, the safety rail 105 may be laid on an outer side of the main line rail 101.
As shown in FIG. 16, in the case of the curved track, a guard member 106 for preventing the wheel from derailing from the main line rail 101 is generally laid on a track so as to be in parallel with the main line rail 101.
FIG. 16 is a plan view showing a working range of the tamping machine, and regions shown by diagonal lines are the working ranges of the tamping machine. As shown in FIG. 16, the tamping work of the ballast 102 by the tamping machine needs to be carried out such that the ballast immediately under the main line rail 101 is tamped in the vicinity of the main line rail 101. However, since the guard member 106 and the safety rail 105 are laid in the working range, these structures need to be temporarily removed before the work of the tamping machine to a place other than the regions shown by the diagonal lines. Then, the structures temporarily removed need to be restored after the work is done.
However, the conventional guard member 106 is laid using a fastening structure including a large number of combinations of bolts and nuts, it is extremely troublesome to attach and detach the guard member 106. In addition, it takes much time and labor to move by hand the guard member 106 that is a heavy product to a place away from the main line rail 101.
The same is true for the safety rail 105. That is, since the safety rail 105 that is a heavy product becomes an obstacle during the work of the tamping machine, the safety rail 105 needs to be moved by hand to a place away from the main line rail 101, which requires much time and labor.
A maintenance work of the main line rail 101 is carried out at predetermined time intervals (for example, once or twice a year) for comfortable ride of trains. In the maintenance work, the main line rails 101 are objectively evaluated by data, such as vibration greatness, a swing direction, and the like of a running vehicle, and if the main line rail 101 exceeds a reference value, a rail grinding work of grinding the main line rail 101 to a predetermined shape by a rail grinding vehicle running on the main line rail 101 is carried out. By the rail grinding work, each of numerical values regarding the vibration greatness, the swing direction, and the like of the running vehicle falls within an appropriate range. The rail grinding work is carried out with respect to not only the track including the ballast but also the main line rail 101 on a slab track according to need.
Since the guard member 106 and the safety rail 105 laid along the main line rail 101 become obstacles during the rail grinding work, the guard member 106 and the safety rail 105 that are heavy products need to be moved by hand to a place away from the main line rail 101, which takes much time and labor.
Moreover, in the case of replacing the main line rail 101, the guard member 106 and the safety rail 105 need to be moved by hand to such a place that the guard member 106 and the safety rail 105 do not become obstacles.
Therefore, the present applicant has filed an application describing that the guard rail is laid along the main line rail using this type of wheel guard apparatus to prevent the wheel from derailing, and the position of the guard rail can be quickly changed to an evacuation position away from the main line rail (see Patent Document 1).
Moreover, the present applicant has also filed an application describing that even if the vehicle has derailed, the derailed vehicle is prevented from seriously deviating from the track, so that the derailed vehicle is prevented from contacting an oncoming vehicle. In accordance with the above application, even if the wheel has derailed, an inner side of the wheel is stopped in the vicinity of a width-direction center of the railroad tie, so that the vehicle is prevented from seriously deviating from the track (see Patent Document 2).    Patent Document 1: Japanese Laid-Open Patent Application Publication No. 2006-328644    Patent Document 2: Japanese Laid-Open Patent Application Publication No. 2006-112215